Diagnostic Policy Service (diagnostic.log): High Disk Usage [Fix]

The Diagnostic Policy Service (DPS) is a Windows service that helps identify and troubleshoot problems with your operating system. It collects diagnostic information and supports Windows troubleshooting tools when something isn’t working correctly.

The diagnostic.log file is associated with diagnostic logging. Depending on the Windows component generating it, diagnostic log files can contain information about system activities, errors, and troubleshooting operations.

When the Diagnostic Policy Service or an associated diagnostic process behaves unexpectedly, it may repeatedly generate log entries or perform excessive background operations. This can contribute to high disk activity and, in some cases, increased storage consumption.

Several factors can cause this behavior, including corrupted diagnostic files, problematic Windows updates, damaged system components, and temporary service glitches.

Before trying the fixes, open Task Manager by pressing Ctrl + Shift + Esc. Select the Processes tab and check whether the Diagnostic Policy Service or another diagnostic-related process is consuming excessive disk resources.

You can also check the Performance tab to see whether your disk usage is unusually high.

Let’s go through the troubleshooting methods one at a time.

Diagnostic Policy Service (diagnostic.log) High Disk Usage

If the Diagnostic Policy Service is causing excessive disk activity on your Windows computer, try the following solutions. 

Start with the first method and move to the next one if the problem continues.

1: Restart the Diagnostic Policy Service

The first thing you should try is restarting the Diagnostic Policy Service. Sometimes, a temporary service glitch causes Windows to perform unnecessary background operations.

Restarting the service can refresh its current state without requiring you to restart your entire computer.

1. Press Windows + R on your keyboard to open the Run dialog box.
2. Type services.msc and press Enter.
3. The Services window will appear, showing the services installed on your computer.
4. Scroll down and locate Diagnostic Policy Service.
5. Right-click the service and select Restart, if the option is available.
6. If Restart is unavailable, select Stop, wait a few seconds, and then select Start.
7. Close the Services window and open Task Manager again.

Now check whether disk usage has decreased.

If the service was temporarily stuck, restarting it may resolve the problem. However, if diagnostic.log continues growing or disk activity remains high, move to the next solution.

2: Clear Temporary Files From Windows

Temporary files can accumulate over time and consume unnecessary storage space. Although they aren’t necessarily responsible for every Diagnostic Policy Service issue, removing unnecessary temporary data is a useful troubleshooting step.

Windows provides a storage management feature that makes this process relatively simple.

1. Press Windows + I to open Windows Settings.
2. In Windows 11, select System and then click Storage. In Windows 10, navigate to System > Storage.
3. Allow Windows a few moments to calculate the storage usage.
4. Select Temporary files.
5. Review the available categories carefully.
6. Select temporary files that you no longer need.
7. Click Remove files to delete the selected items.

Be careful when selecting the Downloads category because it may contain personal files you still need.

Once the cleanup finishes, restart your computer and check whether the disk usage problem has improved.

3: Delete the Diagnostic Log File

If diagnostic.log is continuously growing and consuming a significant amount of storage, you should investigate the file’s location before removing it.

Remember that diagnostic.log is a generic filename. Different Windows components and applications may create files with the same name.

1. Open File Explorer by pressing Windows + E.
2. Navigate to the folder containing the diagnostic.log file. You can also search for the filename using the File Explorer search box.
3. Right-click the file and select Properties.
4. Check its location, file size, and modification date.
5. Identify which application or Windows component owns the file.
6. If it is a temporary diagnostic log that is safe to remove, close the associated application or stop its related service first.
7. Delete the file only if you have confirmed that it is not required by Windows or another application.

If Windows reports that the file is currently in use, don’t force-delete it or change its permissions unnecessarily.

You can restart Windows and investigate the file again. If it belongs to an active Windows diagnostic component, allow Windows to manage it unless you have confirmed that removing it is safe.

Important: Do not delete random files from the Windows, System32, or other system folders simply because their names contain the word diagnostic.

4: Run the System File Checker (SFC) Scan

Corrupted Windows system files can cause different background services to behave unexpectedly. If the Diagnostic Policy Service is repeatedly generating errors, running the System File Checker scan is worth trying.

SFC is a Windows command-line utility that checks protected system files and repairs corrupted versions when possible.

1. Click the Start button.
2. Type Command Prompt in the search box.
3. Right-click Command Prompt and select Run as administrator.
4. If User Account Control appears, click Yes.
5. Type the following command and press Enter:

sfc /scannow

6. Wait for Windows to complete the verification process.

The scan may take several minutes, depending on your system’s performance.

After completion, Windows will display a message explaining whether it found and repaired corrupted files.

If SFC successfully repairs any files, restart your computer and check the disk activity again.

5: Run the DISM Command

If the SFC scan cannot repair corrupted system files, you can use the Deployment Image Servicing and Management (DISM) tool.

DISM checks and repairs the Windows component store, which provides the files required for Windows system repairs.

Follow these instructions:

1. Open Command Prompt as administrator.
2. Enter the following command:

DISM /Online /Cleanup-Image /RestoreHealth

3. Press Enter to start the repair process.
4. Wait until the operation reaches 100%.

Depending on your internet connection and system condition, this process may take some time. Windows may download replacement components when necessary.

Once the operation finishes, run the SFC command again:

sfc /scannow

Restart your computer after both operations are complete.

This method can help resolve system component corruption that might be affecting Windows services.

6: Run the Windows Troubleshooter

Windows includes troubleshooting tools that can identify and resolve common problems with system components.

If the Diagnostic Policy Service is repeatedly recording errors, running the relevant troubleshooter may help identify the underlying issue.

1. Press Windows + I to open Settings.
2. Select System.
3. Click Troubleshoot.
4. Select Other troubleshooters in Windows 11.
5. In Windows 10, open Update & Security > Troubleshoot > Additional troubleshooters.
6. Choose the troubleshooter related to the problem you’re experiencing, such as Network and Internet or Windows Update.
7. Click Run and follow the on-screen instructions.

The available troubleshooters depend on your Windows version.

After completing the process, restart your computer and check whether the Diagnostic Policy Service is still causing excessive disk activity.

7: Check for Windows Updates

An outdated Windows installation or a problematic system component may contribute to service-related issues.

Microsoft regularly releases updates that include security improvements, bug fixes, and reliability enhancements.

To check for available updates:

1. Open Windows Settings using Windows + I.
2. Select Windows Update in Windows 11.
3. In Windows 10, navigate to Update & Security > Windows Update.
4. Click Check for updates.
5. If updates are available, download and install them.
6. Restart your computer if Windows requests it.

After installing the updates, open Task Manager and monitor the disk usage.

If the problem started immediately after installing a particular update, check its update history and investigate whether that update is responsible before considering any rollback.

8: Check Your Disk for Errors

A damaged file system or disk-related problem can also contribute to unusually high disk activity.

Windows provides the CHKDSK utility to scan a drive and identify file system errors.

1. Open Command Prompt as administrator.
2. Enter the following command:

chkdsk C: /scan

3. Press Enter and allow Windows to scan the drive.
4. Review the results for any reported file system problems.

Replace C: with the appropriate drive letter if Windows is installed on another partition.

If CHKDSK reports errors that require an offline repair, follow its instructions. Back up important files before performing repairs, especially if you suspect a failing hard drive.

9: Perform a Clean Boot

If none of the previous methods works, a clean boot can help determine whether a third-party application or background service is interfering with Windows diagnostics.

A clean boot starts Windows with a limited set of drivers and startup programs.

1. Press Windows + R.
2. Type msconfig and press Enter.
3. Open the Services tab.
4. Check Hide all Microsoft services.
5. Click Disable all.
6. Open the Startup tab and select Open Task Manager.
7. Disable the unnecessary startup applications.
8. Close Task Manager and click Apply and OK in System Configuration.
9. Restart your computer.

Check whether disk usage has returned to normal.

If the problem disappears, a third-party application or service may be responsible. Re-enable disabled services and startup applications gradually to identify the source.

Remember to restore your normal startup configuration after troubleshooting.

FAQs

1. What is Diagnostic Policy Service in Windows?

The Diagnostic Policy Service is a Windows background service that helps detect, troubleshoot, and resolve problems with Windows components. It supports diagnostic operations related to networking and other system functions.

2. Why is diagnostic.log using so much disk space?

The diagnostic.log file may grow because a Windows component or application is repeatedly recording diagnostic information. Repeated errors, logging problems, or an application malfunction can contribute to excessive log growth.

3. Is it safe to disable Diagnostic Policy Service?

Disabling the Diagnostic Policy Service is generally not recommended. Windows relies on it for diagnostic and troubleshooting functions. Disabling it may prevent certain troubleshooting features from working correctly. Try repairing the underlying problem instead.

4. Can I delete diagnostic.log?

You can delete a diagnostic.log file if you have confirmed that it is an unnecessary temporary log and that the application or component using it no longer needs it. However, don’t delete system-related logs without checking their location and purpose.

5. Does Diagnostic Policy Service cause 100% disk usage?

It can contribute to high disk activity in certain situations, but it isn’t always the main cause. Other processes, Windows updates, disk errors, background applications, and failing storage devices can also cause 100% disk usage.

6. How do I check which process is using my disk?

Press Ctrl + Shift + Esc to open Task Manager. Select the Processes tab and click the Disk column to sort processes by disk usage. This helps you identify which processes are currently accessing your storage device.